lkml.org 
[lkml]   [2007]   [Jun]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [BUG] ptraced process waiting on syscall may return kernel internal errnos
From
Date
On Thu, 2007-06-14 at 16:58 +0400, Oleg Nesterov wrote:
>
> > Well, the only code path in which we'd want to call cancel_freezing() for kernel
> > threads is when the freezing of kernel threads. However, this only happens if
> > one of the kernel threads declares itself as freezable and the fails to call
> > try_to_freeze(), which is a bug.
>
> But this happens? We know a lot of reasons why try_to_freeze() can fail just
> because some kthread waits for already frozen task.

The freezer is a deadlock-o-matic by design. It's one of the major if
not the main reason why we don't use the code in kernel/power.c on
PowerBooks for suspend-to-ram. I don't like it and paulus hates it.

> Well, we can have very subtle problems because a kernel thread may run with
> TIF_SIGPENDING forever. This means in particualar that any wait_event_interruptible()
> can't succeed. I think this is worse than explicit failure (like -ERESSTART... leak),
> because it is hard to reproduce/debug.

Then just don't send signals to them...

> > Moreover, I'm not sure that it's a good idea at all to send signals to kernel
> > threads from the freezer, since in fact we only need to wake them up to make
> > them call try_to_freeze() (after we've set TIF_FREEZE for them).
>
> Yes! I completely agree.

Sounds like a plan...

Freezer problem 1/102893264 solved.

Ben.


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-06-15 02:09    [W:0.065 / U:0.660 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site